Spring-in

 

A fibre reinforced composite part generally take a shape different from the one that is originally designed after removing from the mould at the end of the curing process although prepregs take the form of the mould during the lay-up stage. Due to the anisotropic nature of the fibre reinforced composite materials, the coefficient of thermal expansion (CTE), the cure shrinkage rate and the stiffness of the lamina are direction dependent. The direction dependent behaviour of the composite materials, with the aid of temperature change during curing, triggers some mechanisms that are responsible for the residual stresses. Also, tool-part interaction, resin flow, initial defects such as fibre wrinkling is some of the other contributors to residual stress. These residual stresses occurring during the curing of composite materials cause distortions at the end of the curing process. Spring-in is one of the distortion occurs during manufacturing.